This invention relates to apparatus for handling the installation and removal of manway covers on the underside of a vessel enclosure where said covers are too heavy to be handled by an unaided individual. In particular, this invention relates to apparatus and a method whereby cumbersome manway covers angularly disposed on the bottom of a vertical tube steam generator vessel can be removed and installed with a minimum of manual intervention. While the invention was made and therefore will be described in connection with the installation and removal of covers employed in steam generators used in nuclear generator stations, it would be of use in other situations where environmental conditions and handling factors make it undesirable or impossible for operating personnel to effect unaided direct manual installation and removal of such covers.
In a typical nuclear powered steam generating installation, a cluster of vertical tube steam generating vessels are disposed around and in the vicinity of a central core structure housing the reactor. The steam generating units of the type in question have on their underside a plurality of very heavy manway covers. Such manway covers are usually angularly disposed at the bottom of the steam generator and can weigh as much as 600 pounds.
Routine servicing requirements as well as other operating conditions necessitate periodic removal of these manway covers from the underside of the generator vessel. In view of the underside location and weight of the manway covers it is not a simple task to remove the cover or to install the same. Removal is currently accomplished with the use of hand operated chain falls, ratchet hoists and brute force. During the removal process, it is necessary to lower the covers a distance of as much as 30 feet to a level surface, given the typical positioning of steam generators within the total plant configuration. Installation of these manway covers also poses difficulty in that once the covers are raised to the underside of the vessel they must be positioned at an angle to the vertical prior to being secured to the manway flange. Present procedure takes a crew of about eight men between two and three hours to remove eight manway covers positioned on the undersides of the four generators in a typical steam generator installation. Reinstallation of such covers requires a considerably longer period of time since the covers must be aligned with bolt holes in the manway flanges. This operation requires the eight man crew to remain in high radiation exposure areas for prolonged periods of time.
U.S. Pat. No. 4,313,709 discloses a device for removing and/or re-installing manway covers on an apparatus under pressure. The patented device is mounted on tracks or rails about which it can traverse in order to assume a position opposite a particular manway cover that is to be removed or installed. In the patented device a hand pump is used for operating a hydraulic actuator to adjust the position of a carriage riding on a vertical shaft. A separate chain hoist is provided for use in lowering a manway cover to a lower level. The patented device is essentially permanently installed and confined to movement along the tracks from location to location. It does not contemplate remote operation.
U.S. Pat. No. 4,360,310 takes a somewhat different approach in order to provide apparatus for manipulating a manway cover. The last mentioned patent requires separate rails to be provided for each manway flange and has a carriage that rides from a horizontal position below the manway flange up on the rail and into juxtaposition with the manway flange. A winch operates a chain or rope for pulling the carriage up and along the rail. Thus, the last mentioned patented device requires rails to be permanently attached to the pressure vessel or the like at each manway opening in order to guide the appropriate carriage between floor and vessel.
Both patented devices are considerably limited in utility both from the standpoint of lack of portability and from the standpoint that an operator is required to work in close proximity to the manway cover being handled. In a nuclear reactor plant, even in the area of the steam generator unit, there is considerable radiation exposure and workers can work in the vicinity for only limited periods of time.
Therefore, it is an object of the present invention to provide apparatus for handling the manway covers in such manner that operators need be in close proximity to the manway cover for only short periods of time and can perform the major portion of the installation or removal of the manway cover from a remote and sheltered position.
It is another object of the present invention to provide a portable handling device which can be installed on sub-frame structures that normally support the steam generator vessel in close proximity to any of the manway covers that are to be handled.